1. Field of the Invention
The present invention relates to a fingerprint input apparatus for irradiating a finger with light from illumination source and receiving the light scattered from the interior of the finger with a solid image pickup device.
2. Related Background Art
With the increasing pervasiveness of economic activities such as electronic trading based on the recent remarkable progress in the information technology, necessity for electronic personal authentication of is also increasing for the purpose of avoiding illegal use of the information.
For electronic personal authentication, there has frequently been employed a method inputting a fingerprint image. However, a system utilizing a total, reflecting prism, as disclosed in Japanese Patent Application Laid-open No. 2000-11142, is associated with drawbacks of becoming large in the shape, and being unable to identify a fingerprint formed for example by molding with a resin.
As a compact and highly reliable fingerprint input apparatus capable of solving theses drawbacks, Japanese Patent Application Laid-open No. 2000-217803 proposes a method of irradiating a finger, maintained in contact with the vicinity of a surface of a two-dimensional solid image pickup element, with a near infrared light and receiving a scattered light from the interior of the finger. This method will be explained with reference to FIG. 10.
In a fingerprint input apparatus shown in FIG. 10, on a surface of a solid image pickup device substrate 1, solid image pickup elements 1a are formed two dimensionally with a predetermined pitch p, on which a cover glass 100 is fixed with a transparent sealing material 41. The solid image pickup device substrate 1 is fixed on a wiring board 3, also is electrically connected by a wire 21 with a wiring 3a on the wiring board 3 and is protected by a sealing resin 41. Also an illuminating LED chip 10 is connected by a wire 12 with the wiring 3a on the wiring board 3 and is protected by the sealing resin 11. A light 10a emitted from the LED chip 10 enters a finger 20, is diffused therein and enters from a fingerprint 20a into the cover glass 100 as a diffuse light 10b. Such entering light arrives, through the cover glass 100, at the solid image pickup element 1a and is photoelectrically converted therein, whereby an electrical signal of a fingerprint image can be obtained. For the LED chip 10, there can be utilized an infrared light, a near infrared light or a red light, but another wavelength region is also utilizable.
The cover glass 100 is required to have an optical filter function, for the purpose of protection from electrical or mechanical destruction of the solid image pickup element 1a caused by a contact of the finger 20 or the like therewith and for eliminating a perturbing light other than the fingerprint image. However, in order to obtain a sharp fingerprint image, the cover glass 100 is required to have an extremely small thickness t, and, for avoiding such situation, it has been necessary to use an expensive material such as a fiber optics plate (FOP).
On the other hand, for attaining a low cost and a compact structure, there is proposed a sweeping technology of moving a finger tip relative to the solid image pickup device and synthesizing continuous plural partial images of such moving finger tip to obtain an image of the entire finger tip (for example Japanese Patent Application Laid-open Nos. 2002-216116 and 2002-133402). In this technology, the two-dimensional array of the solid image pickup elements, which has to be of an area of about the size of the finger, can be reduced to a size only covering the width of the finger, whereby the solid image pickup device and the fiber optical plate can be made inexpensive. In such sweep type, in addition to the optical system explained above, there are also known an electrostatic capacitance system and a thermal detection system.
However, the prior technologies explained in the foregoing is associated with following difficulties in attaining a compact structure and a low cost.                1) In the optical system, since a thickness and unevenness in the adhesion between the protective member and the solid image pickup device affects the sharpness of the image, an unstable adhering method has deteriorated the production yield.        2) Also in adhering the protective member to the solid image pickup device, an adhesive resin is coated in a somewhat excessive amount and the protective member is pressed in order that no bubbles remain in the adhesive and that the adhesive is spread over the entire area. Therefore, at the adhering operation, the adhesive material overflows on the protective member to require a corrective operation such as a wiping operation after the adhesion, thereby lowering the production efficiency.        3) As a chipping of an edge portion of the protective member leads to a crack formation, the protective member has to be cut and handled in stable manner. Particularly in case of a thin protective member, as small pieces have been mounted one by one, such handling has resulted in chipping or cracking.        4) When the protective member is pressed, dusts or foreign substances are incorporated thereunder to cause a damage in the solid image pickup device substrate or a cracking of the protective member, so that an adhering operation in a condition as dust free as possible is desired.        5) As antistatic means is provided in a member of the main body, there result a limitation in the designing and of the main body and a fluctuation resulting from assembling.        
In the conventional methods, sufficient countermeasures have not been made against such difficulties 1) to 5). Also the aforementioned prior technologies do not describe any definite countermeasures or are not satisfactory.